This invention relates to an apparatus for the coating of continuous fibers. It also relates to a method for coating continuous fibers.
Composite materials are widely known and widely used. By combining a polymer with another material, such as glass, carbon, another polymer, or the like, is it possible to obtain unique combinations or levels of properties. Similarly, by combining a metal or glass with selected fibers, it is possible to obtain unique combinations or levels of properties. Advanced composites have evolved as a class of structural materials as a result of the development of high-modulus, high-strength, low-density reinforcing fibers.
The presence of a carbon interlayer along the fiber-matrix interface has been shown to be responsible for the high toughness and strain to failure of Nicalon.RTM. (SiC fiber)/lithium aluminosilicate glass composites and Nicalon.RTM./Ba-Si-Al oxynitride glass composites. However, these composites are not viable for high temperature oxidizing environments. Such environments require oxidation resistant fibers, matrices and interlayers. One approach to fabricating a fiber-matrix interface is to introduce an interlayer as a fiber coating before the composite is densified. After densification, the interlayer chosen should cause crack deflection and fiber pullout similar to carbon interlayers, or should provide oxidation resistance for other interlayers.
Several types or combinations of interlayers are considered to be feasible, including microporous interlayers, reactive interlayers which lose volume, and interlayers with ductile particles. However, application of a coating, particularly a uniform coating, to continuous fibers and fiber tows can be difficult. Measurement of coating thickness can also be difficult.
Several techniques are known for applying coatings to continuous fibers. Fiber coating may be accomplished by passing the fibers through a container filled with a coating liquid, which container has one or more rollers or wheels to keep the fiber immersed in the liquid while coating. One disadvantage of this process is that the fibers must be bent around the roller(s) or wheel(s) and may sustain damage from bending or abrasion. Other disadvantages are that the fibers may be contaminated from contact with the wheel or roller and that fibers which do not tolerate a small bending radius are prone to breakage or require a very large wheel and container.
Coatings may also be applied by spraying. The primary disadvantage of this coating method is that spraying is a line of sight process, so coating thickness is dependent upon the angle at which the spray jet contacts the fiber. Other disadvantages are that spray jets tend to clog easily, the characteristics of the jet may change with time, making control of the process difficult, viscous coating solutions are difficult to apply as a spray, and low viscosity solutions tend to run off the fiber before they are cured.
Fibers may be coated by passing same through a container having a gasket which seals around the moving fiber and prevents coating liquid from flowing out. The disadvantages of this method are that the fiber surface may be contaminated or abraded by contact with the gasket, and fibers having irregular cross-sections or multifilament fibers or tows tend to get caught along irregularities or at broken fibers in gaskets tight enough to prevent leakage of the liquid.
It is an object of the present invention to provide an apparatus for coating continuous fibers.
It is a further object of the present invention to provide a method for coating continuous fibers.
Other objects, aspects and advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of the invention.